In recent years, it is becoming common to mount a head-up display (HUD) device to an instrument panel of a vehicle such as an automobile (e.g., Patent Literature 1). The HUD device projects information (an image) useful to a driver on a combiner or a windshield itself disposed in a direction of a driver's line of sight during driving. The projected image is reflected by the windshield and forms a virtual image. A driver visually recognizes the virtual image overlaid on a front view from the vehicle.
In general, the HUD device has a housing structure and includes a projection light source, which generates a projection light beam, in the housing. The light source generates heat as a result of a light emitting operation. Therefore, it is known to provide a heat dissipating portion to the HUD device to dissipate heat in the housing to the outside through the heat dissipating portion.
To project various kinds of information on the windshield, a projection area of the light beam by the HUD device naturally becomes broad. To form a projection image that is large in display size, it is necessary to secure a long optical path from the projection light source to the windshield. Because the instrument panel and the windshield are close to each other and it is impossible to have the enough light path length between them, it is necessary to secure the light path length by means such as disposing mirrors for reflecting the projection light beam in the housing of the HUD device. Therefore, the HUD device tends to be a large-size heavy-weight unit.
However, the instrument panel easily accumulates heat inside itself because of its structure, which may reduce the HUD device heat dissipating effect by means of the heat dissipating portion. Although it is conceivable to attach a cooling functional component such as a cooling fan, it is difficult to additionally dispose such a cooling functional component in a narrow instrument panel to which the large-size HUD device has been mounted.